Field of the Invention
The present invention relates to a sheet processing device that folds a sheet bundle formed by sheets that are sequentially carried out from an image forming device such as a copier or a printer and accumulated in a bundle and, more particularly, to a sheet processing device that presses a folding loop of the folded sheet bundle so as to prevent sheet bundle from being opened after discharge therefrom.
Description of the Related Art
There are widely known processing devices that align sheets carried out from an image forming device and staple them, or fold them into a booklet. Among them, some processing devices are configured to saddle-stitch the sheet bundle with a staple or an adhesive and fold the sheet bundle into a booklet. Such a device performs folding for sheet bundle formed by about few sheets up to about 30 sheets in two; however, there may be a case where the two-folded sheet bundle is unintentionally opened after being discharged from the device, resulting in reduction in accumulation amount.
Thus, it is widely known that, after the folding, the folding loop of the two-folded sheet bundle is subjected to pressing from thereabove and therebelow.
For example, Japanese Patent No. 4,217,640 (see corresponding U.S. Pat. No. 7,431,274 and U.S. Pat. No. 7,673,862) discloses a device that is moved along a folding loop of a two-folded sheet bundle while pinching/pressing the folding loop by means of pressing rollers disposed above and below the folding loop. This device is also provided with a flattening roller that presses the folding loop from a front side thereof at a position slightly rearward of the pinching/pressing position of the upper and lower pressing rollers. That is, in this device, the pressing rollers that pinch/press the folding loop from thereabove and therebelow and flattening roller that presses the folding loop from the front side thereof are formed into one unit, and this unit is moved along the sheet folding loop. Thus, a portion that is pinched by the pressing rollers can be made flat, thereby reducing wrinkles and breaks of the folding loop due to a difference in gripping force.
Further, as illustrated in detail in FIGS. 11 and 12, Japanese Patent No. 4217640 discloses, as a device of a second embodiment, a device in which a unit provided with a pair of pressing rollers that pinch/press the folding loop from thereabove and therebelow are provided in two rows before and after a flattening roller that presses the folding loop from the front side thereof is moved along the folding loop of the sheet bundle. The unit thus configured is moved from an outside of one end portion of the sheet bundle in a width direction thereof toward inside thereof and is passed through the other end portion thereof while pinching/pressing the folding loop by means of the pressing roller pairs to thereby flatten a back-folded portion.
Further, Jpn. Pat. Appln. Laid-Open Publication No. 2014-76903 (see corresponding U.S Patent Publication 2014/077436A1) discloses a device provided with a pair of pressing rollers that press a folding loop of a two-folded sheet bundle in a sheet thickness direction and a moving unit that reciprocates the pressing roller pair in a sheet width direction. This device is configured to move the pressing roller pair between a position where they are separated away from each other and a position where they are brought into pressure contact with each other. Upon performing additional folding for the sheet bundle, the moving unit is moved inward from an end portion of the sheet bundle with the pressing roller pair separated away from each other and then presses a fold (folding loop portion) of the sheet bundle by means of the pressing roller pair at the inside position. After the moving unit has passed through one end portion, pressing by the pressing roller pair is released to separate the pressing roller pair away from each other. When being moved again, the moving unit is passed through the one end position of the sheet bundle with the pressing roller pair separated away from each other, then presses starting from the inside position by means of the pressing roller pair, and passes through the other end portion of the sheet bundle. In other words, the pressing against the folding loop of the sheet bundle is started from the inside position in the sheet width direction to the one or the other end portion of the sheet bundle.
The above-described devices that perform the additional folding for the folded sheet bundle carried out from an image forming device or the like have the following problems, respectively.
In the device disclosed in Japanese Patent No. 4,217,640, the roller pair that is previously brought into a pressure contact state is moved along the folding loop. When the pressing roller pair is assembled to the moving unit, it is necessary to individually mount the pressing rollers, springs for biasing the pressing rollers, and a pressurizing arm disposed between the spring and the pressing roller to the moving unit, thus taking much time and trouble for assembly. Further, even if the roller pair is reciprocated along the folding loop many times, the roller pair presses the same position, that is, the folded positions are overlapped in a straight line, with the result that the folded sheet bundle may be opened after the pressing. Thus, an accumulating property of the folded sheet bundle cannot be effectively improved.
Similarly, in the device disclosed in Jpn. Pat. Appln. Laid-Open Publication No. 2014-76903, when the pressing roller pair is assembled to the moving unit, it is necessary to individually mount the pressing rollers, pressurizing springs for biasing the pressing rollers, and a spring bracket disposed between the spring and the pressing roller to the moving unit, thus taking much time and trouble for assembly.
Further, in this device, the pressing roller pair are separated from each other at a standby position outside the folded sheet bundle in the sheet width direction, then moved to the inside position of the folded sheet bundle (where the folding loop exists) in the sheet width direction while being kept in the separated state, and is then made to perform the additional folding at this position by being brought into pressure contact with each other. However, the roller pair presses the same position in the additional folding for the folding loop, that is, the folded positions are overlapped in a straight line, with the result that the folded sheet bundle may be opened after the pressing. Thus, it is difficult to improve the accumulating property of the folded sheet bundle.